Wireless mesh networks are increasingly used to provide inexpensive network connectivity in unlicensed spectrums. Examples include municipal wireless fidelity (WiFi) networks that provide cheap Internet access and wireless sensor networks (WSNs) that provide low cost process monitoring and control capabilities for industrial facilities.
Routing in these types of wireless networks often plays an important or critical role for applications to deliver high-performance and highly robust services. However, routing in these types of networks often exhibits distinctive characteristics compared to wireline networks (such as Ethernet networks), infrastructured wireless networks (such as cellular telephone networks), and even many ad-hoc wireless networks (such as MANET networks). Some characteristics of these types of wireless networks that can significantly affect routing protocol design include: highly lossy links (such as less than 50% successful transmissions); small packet size (such as less than 50 bytes); time-sensitive data; and large and dynamic network sizes.
Conventional protocols used in these types of wireless networks generally suffer low data throughput due to many inevitable link-level retransmissions caused by the low link quality. Conventional protocols also respond poorly to network dynamics since they need to maintain information on global paths from sources to destinations. For instance, current techniques typically require the maintenance of global information (such as global forwarder lists), which means these techniques are not easily scalable. Further, large batch sizes can make current techniques inefficient in handling small data payloads, and current techniques are often unsuitable for routing of time-sensitive data (which is commonly seen in WSNs).
In addition, current techniques typically suffer a fundamental misuse of path metrics that can be important or essential for the evaluation of “distances” to destinations. Current techniques often use Expected Transmission Count (ETX), which uses an expected number of transmissions to measure a link cost and a minimum cost of all possible paths as the path metric. ETX has been widely used in best path routings, where the single shortest path is used for all data forwarding. However, ETX is clearly a mismatch when used with opportunistic routing, which by nature forwards data on multiple paths non-deterministically and potentially simultaneously.